The above referenced pending application discloses ways to improve interfacial chemical reactions by preheating the workpiece, prior to its entry in a given processing solution, to a temperature higher than, or equal to, the temperature required for a given interfacial reaction to take place.
While above pending application envisions a broad scope of improving interfacial chemical reactions in general, it mainly focuses on, and exemplifies electroless plating of copper, especially as it relates to the manufacture of through-hole plated PCBs.
Also, above pending application, by virtue of principally being described in terms of electrolessly plating PCB laminates constructed from organic polymer composites, is dealing with preheating temperatures generally below or around 100 deg. C, mainly because of potential thermal degradation of polymers used in construction of PCB composites.
Thus, the above referenced pending application does not fully live up to its potential of specifically embodying more elevated preheating temperatures, i.e. approaching or exceeding temperatures of 100 deg. C and above. Such elevated temperatures are indeed practicable with heat-resistant workpieces, such as metals, refractory materials, and the like.
Interfacial technology is a very broad field, covering a vast and varied range of industries such as cleaning, stripping, electrophoretic painting, blackening of metals, metal plating powders such as diamonds, to name only a few. Thus, the Electrochemical Society issues a publication called xe2x80x9cInterfacexe2x80x9d, almost exclusively devoted to interfacial applications. While above publication is referenced mainly as a means of illustrating the technology of interfaces, it is also indicative of the prior art.
The objective of this invention is to improve, facilitate, speed up, interfacial chemical reactions, by preheating the workpiece to temperatures preferably at about or above 70 deg. C, more preferably at about or above 100 deg. C, prior to its entering a given processing solution. Conceptually, one will be guided by optimal temperatures that a given interfacial reaction demands, such temperatures being determined by what is needed by the desired interfacial reaction, without however exceeding maximum temperature tolerable for a given substrate material.
The method of the present invention may be applied to both metallic and non-metallic substrates.
Hence, this present application continues and complements above pending US application #2002/0086102A1, by pointing out and exemplifying heating temperatures as convenient/needed to optimize a given interfacial reaction, such temperature being limited only by what the substrate can bear without degradation or impairment
In a preferred embodiment of the invention, the preheating of the workpiece to an optimal temperature, coupled with suitably designed accommodating composition and solution temperature, will lead to Ultra Fast Interfacial Reactions (UFIR), with significant potential for improved surface reactions.
It is noted that while the above-referenced pending application uses the term xe2x80x9cpre-heating the workpiecexe2x80x9d prior to being contacted with a given processing solution, it does not exclude preheating the workpiece, and also keeping it heated or xe2x80x9chotxe2x80x9d for the duration of the interfacial reaction., if continued heating of the workpiece is beneficial in instances as they may arise.
Thus, in this application, which is a continuation of the one that is pending and referred to previously, pre-heating and heating are interchangeable and within the scope of pending application. The invention is principally directed to reactions that involve contacting solids with liquids (S/L), and is not directed to other interfacial reactions, for example solid/gas and liquid/gas.
Further, a preferred embodiment of the invention primarily envisions interfacial reactions involving solids contacted with liquids comprising aqueous solutions, emulsions, microemulsions and the like, without however excluding organic, non-aqueous solutions.
Again, the application envisages interfacial reactions generally involving solid workpieces regardless of their shape and material of construction, with the latter comprising metals, refractory materials or composites thereof, non-conductors or semiconductors as in silicon-bearing electronic devices in general and wafers in particular, powders made of metals, non-metals or combinations, fibers as in optical fibers, synthetic textiles, and the like.
Regarding the optimal preheating temperature, it will be best obtained by trial-and-error, being generally guided by the nature of the workpiece or substrate, the characteristics of the interfacial reaction, its kinetics, etc., again without such heating temperatures exceeding the highest that is allowable for a given material that the workpiece is made of.
The invention will benefit most, if not all type of interfacial reactions, and is not limited to electroless plating, surface finishing, and the like, though it may be principally exemplified via the latter, for the sake of convenience.
As to the method of preheating/heating the workpiece prior to its entry in a given processing solution, it will generally be selected on the basis of the raw material it is made of, its shape, thermal conductivity, the nature of the interfacial reaction, etc. While some potential methods of heating the workpiece are partially outlined in the pending application referenced previously, additional methods are of course at the disposal of one skilled in the art, namely radiation-induced heating such as IR, induction, microwave, etc. that in many processes may well be the method of choice.
Thus, the invention may especially benefit the processing of interconnect devices, LCD""s, silicon wafers, optical fibers, integrated circuits, CMP planarization, to name some typical ones that are currently in the forefront of technological endeavors.
The advantages of the invention reside primarily, though not exclusively, in affording lower operating temperatures of processing solutions conducive to longer solution life, savings in energy, use of solution compositions comprising chemical compounds that are environmentally objectionable at elevated solution temperatures, etc. Additionally, the invention envisions reactions promoted/aided by xe2x80x9chotxe2x80x9d solid/xe2x80x9ccoldxe2x80x9d solution interface, where such reactions may not be easily obtained with unheated, i.e. xe2x80x9ccoldxe2x80x9d solid/solution interfaces of the prior art. While generally dealing with lower than recommended solution or bath temperature, the application does not exclude preheating the workpiece concurrently with heating the solution temperature as well, if the latter leads to further benefits, i.e. when interfacial reaction speed is of essence.
In addition to advantages/benefits that have been pointed out, potentially further ones, perhaps unforeseen, will emerge as the patent becomes available to, and is practiced by those skilled in the art.
The invention and its potential will now be partially illustrated in the ensuing examples.